Standing seam metal roofs have been in existence for hundreds of years. This roofing system uses panels having a generally flat pan portion and upstanding lateral edges. The upper ends of the adjacent edges are usually folded over into what is called a double lockseam. Standing seam roofs are commonly secured to the structure in one of two ways. One way, as shown in U.S. Pat. No. 102,441, drives screws or other fasteners through the pan. This has the disadvantage of providing a place for leaks and also limits the length of the pan because of thermal expansion and contraction. More commonly cleats or brackets are used to secure the panels to the structure. Conventional cleats are secured to the structure at their lower ends and have their upper ends folded into the lockseam when the double lockseam is formed thus fastening the panels to the structure.
The double lockseam of standing seam roofing systems were initially made by the roofing artisan using metal tongs or hand seamers and mallets. In the early 1970's several manufacturers developed and sold manual or power driven seaming machines for accomplishing this. One such standing seamer is sold by KMF Equipment Corporation of Huntington, Pennsylvania. Such powered seamers have effectively replaced hand seaming.
Most, if not all, roofing panels are now manufactured by roll forming machines. Factory manufactured roofing systems usually include panels supplied in 40 foot lengths, the length of common carriers. Alternatively, the panels can be formed in continuous lengths at the job site using mobile roll formers. In either event, thermal expansion and contraction of these relatively long panels must be accommodated by the method of attachment of the panels to the roof. One system, designed for ease of installation and for accommodating the thermal expansion and contraction which arises with the longer length panels, is made by Butler Manufacturing of Kansas City, Mo., and is sold as the MR-24 System and Clip. Another system, also designed to allow for some thermal movement, is shown in U.S. Pat. No. 4,184,299 to East. The Butler system employs the double lockseam while East uses a separate snap-on cap. The amount of movement permitted with the East system is determined by the length of the slot and the bracket.
There is a problem common to standing seam roofing systems which by their design do not create a seamed or folded region, such as the system shown in the East patent or U.S. Pat. No. 4,114,340 to Dean, et al. The lack of a lockseam creates a joint between the panels that is at best difficult to seal effectively. Under packs of snow or ice or in the event of wind driven rain, capillary action can allow moisture to be drawn up and over the vertical flange and into the void between the panel. The double lockseam of conventional standing seam roofing systems substantially eliminates this problem. To create the tightest joint, it is desirable to fold or form the metal as close to the hold down bracket or clip (which is folded into the standing seam) as is possible. This helps prevent water infiltration by capillary action. However, there are always small voids at the edges of the brackets which are sites for possible capillary action. To prevent this, sealants can be used, such as shown in the patent to Siddons. Although double locked standing seams eliminate much of the problems due to water infiltration due to capillary action, and although use of sealants can effectively control the problem of leakage at the hold down brackets, the intermittent positioning of the cleat or bracket causes a bulge or bump along the standing seam. This is not only visually unappealing, it also causes pre-painted surfaces to crack or split which lowers the aesthetic appeal of the roofing system and reduces somewhat the protective value of the paint.